Alzheimer disease (AD) is the most common neurodegenerative disease in the world. The relationship between AD and homocysteine (Hcy) is contradictory.A community-based investigation was conducted to find patients with AD in a vitamin B deficient population (≥55 years old) in Lüliang area in China. Venous blood samples were collected. Serum Hcy, folate, and vitamin B12 were measured. For each case, 4 controls were selected matched with age to evaluate the relationship between Hcy and AD.The crude prevalence of AD among people ages 55 years or older in this area was 8.60%. There were significant differences in serum Hcy and B12 between the case and control groups. We found that the higher level of serum Hcy was associated with a high risk of AD, and higher education level, higher folate and B12 concentration were protective factors to AD.Adjustment of diet structure and supplementation of folate and B12 may offer potential therapeutic measures in this area.